1. Field of the Invention
The present invention relates to a method of collecting data from an optical channel monitor which monitors the power of wavelength-division multiplexed light at each wavelength.
2. Description of the Related Art
With expansion of the application of wavelength division multiplexing (WDM) technologies, there is a growing demand for optical channel monitors as a means for directly monitoring the level of a light signal at each wavelength within a transmission fiber line without multiplexing/demultiplexing the signals.
Optical channel monitors are roughly divided into two types. One is a monochromator type wherein an optical filter which is equipped within the monochromator, is swept in wavelength and the output of the filter is received by a photo-detector to monitor the level at each wavelength of incoming light. The other is a polychromator type wherein a plurality of photo-detectors are placed at the demultiplexing side of a wavelength demultiplexer such as a diffraction grating and wherein the level of the signal received by each detector is swept to monitor the light level at each wavelength of incoming light.
For example, JP2006-286918A discloses an optical amplification device for use in a wavelength division multiplexing system. This patent literature describes that first, second, and third optical dividers are mounted in order from an input end to an output end of the device; the powers of signal lights having different wavelengths are monitored at the branch path of the second optical divider; and are measured for each wavelength by means of an optical channel monitor which is connected to the branch path of the third optical divider.
Both types are unable to simultaneously monitor the signal lights of every wavelength within a transmission line fiber. Accordingly, these types are problematic in that when the level of incident light to the optical monitor undergoes a change due to, for example, a fluctuation of the light level in the transmission line during the sweeping operation, the error of the data measured during the fluctuation becomes large. This can lead to the malfunction of a transmission apparatus which accommodates the optical channel monitor because it performs alarm operation etc., based on the result of detection of the optical channel monitor. Further, in order to prevent the aforementioned malfunction, processing such as averaging of the monitored values is required, resulting in sacrificing the response speed of the optical channel monitor.